High-frequency-amplifying apparatus



April 1931. w. L. CARLSON ET AL 1,301,138

HIGH FREQUENCY AMPLIF YING APPARATUS Filed June 22, 1928 Inventors wefldelhL-carrlson Ken th A-Chtttick, b

Thew Attorney.

Patented Apr. 14, 1931 v UNITED STATES PATENT OFFICE WENDELL L. CARLSON, OF SGHENECTADY, AND KENNETH A. CHIT'ILICK, OF SCOTIA, NEW YORK, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK HIGH-FREQUENGY-AMPLIFYING APPARATUS Application filed June22, 1928. Serial No. 287,563.

The present invention relates to a high frequency amplifying apparatus embodying electron discharge devices, and has for its object to provide an improved apparatus of this character whereby a high overall selectivity and amplification, a controlled overall regeneration, anda high operating .efliciency are realized. While not limited thereto, the amplifying apparatus of the present invention is 19 adapted for operating at a relatively high fixed frequency or frequency range, whereby it may readily be used as the intermediate frequency amplifier means of a superhetrodyne receiver of radio frequency orbroadcast signals. i

The invention will be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, the figure is a wiring diagram of a high frequency amplifying appa ratus embodying the invention. For convenience in referring thereto hereinafter and in the claims, this apparatus will be termed an amplifier.

Referring to the drawing, 5 and 6 are the input and output terminals respectively of the amplifier, between which are connected a series of amplifying stages 7, 8 and 9and an output stage 10 outlined by the dotted rectangles which may be taken as representing suitable metal containers or stage shields.

Each stage contains a suitable electron discharge amplifying device 1 1 having an input or grid circuit 12 tuned to a desired frequency by suitable means such as an inductance 0r coil 13 and variable capacity 14, and having a plate or anode circuit 15 coupled with the grid circuit of the next succeeding stage by means hereinafter described. In the case of the last or output stage, the plate circuit leads to output terminals 6 and is completed through apparatus with which the amplifier may be used. The amplifier receives the signal to be amplified at the initial stage 7 through input terminals 5 and a suitable coupling means such as a coil 16 associated with the initial grid circuit.

17 and 18 are the cathode supply leads for the amplifier which may be connected to any suitable source of current. Lead 17 is the common return lead for the grid bias and plate or anode supply and in the present example is connected with batteries 19 and 20 which are provided respectively as the sources iqf grid bias and anode voltage for the ampli- Each grid circuit receives biasing voltage from the biasing means 19 through a common bias wire 21 and separate impedances or resistors 22 which are bypassed directly to common cathode return lead 17 by bypass capacities 23 in each stage except stage 10 which is not provided with a direct bypass capacity. Impedances or resistors 22 and bypass capacities 23 are of suitable values to prevent any undesired coupling with or between the grid circuits having a common bias means. To this end the grid bias supply means is also preferably shunted by a relatively large fixed capacity 24 to the common cathode lead 17 The plate or anode supply means 20 is connected with a common supply wire 25 and is preferably bypassed also by a relatively large capacity 26 to the common cathode return lead 17. Each plate or anode circuit 15 takes energy from the supply wire 25 through a separate tuned impedance preferably in the form of a simple reactance choke coil 27, the high potential end of which is bypassed by a condenser or capacity 28 to the common cathode return lead 17 in each stage. The tuned impedance or reactance choke coil in each stage is of such inductance and distributed capacity that its frequency response period is substantially that for which the amplifier is tuned, while the bypass capacity is preferably relatively large, forming a low resistance high frequency return path to the cathode circuit. This provides in effect a tuned anode supply lead for each stage, the high potential or anode end of which is shunted to the cathode circuit by means providing a low resistance high frequency cathode return path.

In providing the proper reactance choke coil as the impedance in each anode supply load, we have found that the least coupling through the common supply means occurs when a certain number of turns is included in the coil, a greater or lesser number increasing the coupling or coupling voltage impressed across the supply means. The proper number of turns is found to be such that the natural period of the -coil, occasioned .by its inductance and distributed capacity, is substantially equal to the frequency for which the amplifier is tuned. The coupling between the various stages through the common "anode supply source is then at a minimum. 7

A coil wound with a proper number of turns to give it a natural frequency response period, substantially equal to that for which the amplifier is tuned, provides a irelatively simple impedancemeans in the circuit, and

without the use of additional shunt capacity, the distributed capacity of itheicoil 'is sufiicientto affect the :tuning o'f the coil. -.With this arrangement a maximum inductance with a minimum capacity is utilized aandthe result is a highly effective impedance in the circuit. '7 r r In providing a :coil of this ch a-ract-er, the turnsof the coil; are increased and decreased until a maximum i pedance i additional shunt capacity is .used, this frequencyis the naturahresponse periodor frequencyof the coil, and when placed .in'circuit with the anodecsupply meansiit offers a maximum ,in pedanceto that frequency. [A greater or .a lesser .numberiof .turns .than the number required to bring the natural frequency response period-to substantially that of :the other tuned. circuits has been :found to make the impedance effect less tlran1naximum,:although the value of the. bypass capacity is not critical, .but should be relatively high.

' By wayof example may be-statedthat inconnection with an amplifier-of the character described for .a signal frequency .of 3,000 K. (1, We have found .that .a suitable choke coil for I each anode supply v lead may be provided bya universally .Wound coil .of about 100:turns having an insidediameter of about ofaninchand havinga thickness of about A; of an inch. The numberofturns will vary slightly witheach coil because of slight variations in the spacing of the turns or the thickness of .the insulation which slightly changes .the distributed capacity of each coil. 3

, In this tuned impedance arrangement the .interstagecoupling portion .or active portionofeachanodeor .plate circuit '15 is connectedat a supply point terminal 29in each stage with the high potentialzend of the inductance or choke,27 and with the bypass capacity 28. i Y

. Inthe several stages each interstage cou :pling portion of the anode-circuit of a preceding :stage is arranged :to ,reactupon the operate, that is to the input frequency applied at terminals 5. i

The low potential side of the circuit, adj acent supply terminal 29, is extended intm'the nextstage and-is there coupled with-thergrid circuit of that stage by a coil 32. The latter coil "is "preferably'o'fonly a few turns, pr0- Viding optimum coupling with the grid circuit or coilof the second stage and arranged to provide. no appreciableelectrostatic or 'capacitycoupling therewith. -It .is .in circuit with and forms partcf'inductance 30. By optimum 1 couplingias used above .and hereinafter and in .the claims, {the commonlyaccepted meaning .ofthe .term is .to .be .understood, that is, acouplinggiving a maximum voltage amplification with a maximumselectivity. This-maybe,providedlbyarelatively close magnetic couplingand.aminimumoelec trostatic coupling.

node

circuit to the impedance of the electron dis charge :device :and .to provide an increased selectivity which is:alsonnateriallyincreased by the useof optimum coupling with the next-stage through coil .32. I

The plate or anode circuitoftheamplifye ing device in the secondstage '8' leads into the next vtor :third stage .9 and is divided to neutralize the overall regenerationofthe .amplifier. .In this arrangementtheicouplingeor plate coil is divided .into two equal or substantially equal parts and 36 whichare loosely coupled toeach-other in .order'torobtain azcertain amount of .regenerationjin Stage 8, the regeneration beingadjusted :to the desired .value by spacing the turns'of coils 35 and :36 .or varying the .nunriherof turnsineach. v v 37 is the neutralizing capacitylconnec'ting coil 36 with the a grid circuitof .the amplifying device of stage v8. -'Ishis.ca,pac'ity.ismadc equal to the anode-grid capacity .of .the .3111: 'plifyingdevice of this stage, and with .both sections of the plateoranodecoil connected with the common supply terminal 29 ,pro- 'vides a neutralizing arrangement differing from the=usual type.of.indiVidualstage.neu- .tralizingkcircuit.

In this case individual stage neutralization is not desired but an overall .neutralizaample byrthe divided plate .coil, :thextwo high ,potential .end .34 thereof .to adapt the halves of which are arranged in spaced relation to each other on opposite sides or ends of the grid coil of the next stage as indicated in the drawing. With this arrangement, any desired degree of close coupling with the next grid circuit is obtainable by varying the spacing between the plate or anode coils and the grid coil, while changes in the neutralizing effect is made by adjusting the spacing of the halves of the split anode or plate coil. While the amplifier is thus neutralized against'overall feed back regeneration, the desired amount of regeneration in stage 8 is obtained by suitably spacing the turns of each half of the plate or anode coil or changing the number of turns therein as hereinbefore mentioned, an increase in the number of turns or a closer relation between the turns tending to increase the regeneration.

The plate or anode circuit of stage 9 is made a part of the tuned grid circuit of the output stage 10. That is, this anode circuit leads through a coupling'coil 38 which is in effect a part of coil 13, being connected in series therewith through a coupling condenser or capacity 39, and connects with plate supply terminal 29. Capacity 39 isolates the grid circuit from the high anode voltage and should be of relatively low resistance to the frequency to which the grid circuit is tuned.

This last circuit arrangement in effect eliminatesone coil and results in lower losses and higher selectivity for the reason that a separate primary with its dielectric support is eliminated, together with the dielectric and capacity losses therein. This is especially desirable in the output circuit wherein the amplified frequency is relatively great, that is, in the order of 3,000 K. C. for example.

In its arrangement this circuit is similar to the tapped tuned plate or anode circuit of the initial stage 7 except the coupling is closer since the coupling coil and grid coil are each in the same tuned circuit, instead of being separate and coupled by a coil of few turns.

Hence in connection with the first and last stages, substantially the same tuned selective coupling means is used, while the second or intermediate stage is provided with an untuned coupling means providing a desired amount of stage regeneration and a neutralized overall regeneration. As described hereinbefore, each anode circuit is provided further with a tuned supply circuit having a high impedance to the signal being amplified; hence the coupling between the stages is confined to the intended means as provided.

Considered in one of its aspects, the amplifier comprises a series of tuned grid circuits coupled with tuned input and output anode circuits and an intermediate anode circuit adapted to neutralize the overall regeneration of the amplifier. Considered thus the electric discharge device in stage 10 is merely a coupling device for external apparatus which may be connected with output terminals 6.

This arrangement thus makes the amplifier well adapted for use on any high frequency apparatus where high amplification of a definite signal to the exclusion of others of different frequency is desired. Thus while it is not limited thereto, it is particularly suited for use in a superheterodyne receiver as the intermediate amplifier. As such it is well adapted to be employed in connection with apparatus shown and described in a copending application of H. C. Allen and W. L. Carlson, Serial No. 241,941, filed December 22, 1927.

What we claim as new and desire to se-' cure by Letters Patent of the United States 15:

1. In a high frequency amplifier embodying electric discharge devices, the combination of means providing tuned input and output anode circuits therefor, and an intermediate divided anode circuit including a pair of spaced coupling coils adapted to neutralize the overall regeneration of the amplifier.

2-. In a high frequency amplifier embodying electric discharge devices, the combination of a tuned input and a tuned output anode circuit, an intermediate divided anode circuit adapted to neutralize the overall regeneration of the amplifier, a supply circuit for each of said anode circuits, and an impedance means in each of said supply circuits, said impedance means and anode circuits being tuned to substantially the same frequency.

3. In a high frequency amplifier embodying electric discharge devices, the combination of a tuned input and a tuned output anode circuit, an intermediate divided anode circuit adapted to neutralize the overall regeneration of the amplifier, a supply circuit for each of said anode circuits a choke coil in each supply circuit, the natural frequency response period of which coil is substantially equal to that of the tuned anode circuits, a cathode return lead, and a bypass capacity connecting the high potential end of each choke coil with said cathode return lead.

4. A tunedhigh frequency amplifier employing a plurality of electric discharge amplifier devices and having an initial and a subsequent stage, the anode circuits of which are tuned, one of said anode circuits including a coil of relatively few turns having optimum coupling with a tuned circuit of the amplifier, said amplifier having an intermediate stage, the anode circuit of which includes two spaced coils substantially equally coupled magnetically with a tuned circuit of the amplifier, and means providing a tuned anode supply lead for each stage adapted to offer a maximum; impedance to the fre quency for which the anode circuits are tuned. v

5. A. tuned high frequency amplifier-employing a plurality .ofelectricdischarge ainpl-ifier devices, said. amplifier havingjan lnltialand a subsequent stage, the anode .cir-

cu its of which are-tuned, and .an intermediate stage, the vanode circuit .of which includes two spaced coils substantially equally coupledmagnetically with a tuned circuit of they-amplifier, andmeans providing a tuned anode supply lead for each stage, the natural frequency response ,period of Which is substantially equal to that of said tuned anode circuits. 7 v I GPA tuned high frequency amplifier employing a plurality of electric discharge amplifie'r devices, said amplifier having an initial and a subsequent stage, the anode circuits ofwh'ich are tuned and each adapted to the impedance of the electric discharge device withwhich it is .in-circuit,\one of said circuits including a coilof relatively few turns havingioptiinum coupling with atuned circuit of the amplifiers, said amplifier having an intermediate stage, the anode circuit .ofwhich includes tWo spaced coils substantially equally coupled magnetically With a tuned circuitiof the amplifien-ananode supplylead foreach stage, a choke coil in each of said leads, the natural period of which coil is substantially equal to that of said tuned ancdecircuits, and a bypass condenser connected with the anode end of eachxof said supply leads.

. 7,. In a high frequency amplifier embodying electric discharge devices, the combination of a tuned input and a tuned output anodecircuit, an intermediate-divided anode circuit adapted to neutralize the voverall regeneration; of the amplifier, a supply circuit forleac'h o f said anode circuits, .andza choke coil in each of saidasupply circuits, the

naturalvperiod of which coil i-s-substantially equal to that of the tuned anode circuits.

8. In a high frequency-amplifierembodyingielectric discharge'devices, the combination of a tuned input and a tuned output anode circuit, an interinediatedivided anode circuitadapted to neutralize the overall regeneration of the amplifier,-.a'supply circuit for each of said anode circuits, .a choke coil in each of said supply circuits, the natural period of which coil is substantially ,equal .tothat ofthe-tuned anode circuits, and means providing a cathode return lnwitness whereofwe have hereunto set .ouinhands this 2lst-day of June, 1928.

WENDELL L. CARLSON. KENNETH a. ionirrioK,

low resistance high frequency path fromthe high potential v'endof-said coil. 

